Piston type sound generator



March 4, 1952 Filed Sept. 2, 1949 c. B. HORSLEY ETAL 7, 3

PISTON TYPE SOUND GENERATOR 2 SHEET$SHEET 1 frzverz tam, Gordmz C. Seaway, a Berta BJyOTSZLy,

March 1952 c. B. HORSLEY ETAL 2,587,848

PISTON TYPE SOUND GENERATOR Filed Sept. 2, 1949 2 SHEETS-SHEET 2 6y 2: Atty.

Patented Mar. 4, 1952 Gapertom B. Horsley, westwood and Gordon 0.. S.eavey,.Arlington, Mass.,, assignors to Sonic. Research, Corporation; Boston, Mass, azcorporation-.otMassachusetts Applicationvseptemlier 2, 1949', Serial No; 1133686 6. Claims.. (01. 116-137) This invention. relates to a: sonic? apparatus..ot

thetypeinwhich sound is produced by alsurfaceof a periodically oscillating body which;.is; 1118:-

chanically driven. In one.- preferredeembodiment theinvention is exemplified bya sonic? apparatus" for treating gases and for-agglomerating or:fioc.- culating particles. or droplets suspended in av gaseous. medium.

In producingsound by mechanicallyoscillating. a. body, an immediate problem'is the development of high bearing loads in the. equipment whichris employed to actuate the. oscillating. body and thusto produce sound-when operating. atvintensi ties which are suitablefor. commercial applications. Meanshave been proposed :for reducingbearing loads in. connection, with. sonic treatment of liquids where it is possible. to: take advantage of theinertial and elastic effects inherentin a liquid body which is being treated. A similar advantage cannot ofcourse be. realized to. any appreciable extent when dealing with a gaseoustype body;-

An object of the invention therefore is to deal with the problems indicatedand to devise-an improved sound generating apparatus in which practica] and eflicient means are incorporated for overcoming to a very large extentthe forcesthat would otherwise. cause excessive bearing loads, especially with reference. to treatment of gaseous bodies.

These and other objects and noveliea-tures of the invention will appear from. the following, description of a preferred embodimentof. the invention, selected for purposes of illustration and shown in the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of thesonic apparatus employed in the invention, including. a soundgenerator and achamber;

Fig- 2. is a central cross section taken on the line. 2-2 of. Fig. 5il1ustrating. the. sound. generate ing apparatus ofthe inventionwith a sectionof. thechamber being illustrated.fragmentarily at one side thereof;

Fig. 3 is a cross section taken on the. line133 of Fig. 2;

Fig, 4 is a view taken on the line 4 -4. ofFig. 2; and

I Fig. 5 is a view taken on..the. line'.':--5.o.fiE'ig.

2 to. more clearly indicate. the crankmechanism.

The, general. plan. of. thezrsoundlgenerating ap.-- paratusof the inventionincludes a spring mechal-- nism useful in reducing; bearing loads, combined with a piston which is arranged. to. oscillatein'a position. of the closed. chamber. In.thacombination.thesohalpe berrrepresent'sr an: enclosure: having. a: lengtmsumstantiallyaequalzto amultiple ofhalf of. the-{wave length of? sound in the. gaseouszmedium; to. be. treated: at: the operating frequency. The-piston is located at. one. end. of. the :chamber and. spring:

means are'operatively connected to. the piston so that the. natural frequency of oscillation-oil the piston is substantially thesame as, theoperating, frequency. The. driving mechanismis connected to the piston through. onespring; member which. is. substantial'y weaker than the spring means which. determine the natural; frequency of. oscil lation of the piston.

Considering. in greater detail. the. embodiment of. this combinationas shown inathe accompanyingxdrawings, I. denotes thesound chamberqwhich may: be: mounted; on any conventional type, of.

base. such aspthe supports. shown and whichis provided with aninlet Zandan outlet 3 by means ofgwhich: a gaseous: medium such as for example an aerosol may be. introduced into the chamber. I: and discharged after hav-ing sbeen processed.

One end of the chamber is. closed as shownin Eig. 1., whileaa pistondic is;mounted forreciprocationat thevopposite end, asshowninFig; 2. The piston end ofithechamber is formed with a flange section. 5 to which is securedby fastenings 61a housing 1 extending rearwardly oi. the: chamber. A'ring 8- is received and. held betweenthe. housing and; the flange 5; and: in turn support in a. groove therein.a-..flexible-annu1ar-sealingmember;a. The

inner circular-edge: of: the; sealing member 9: en-

gage with the" piston; and is fitted into a second. ring lflcarried; in pl'stonv 4. The-ring: I0; is held.

in place-:by an. annular retainingmember H. It'

istnot intended that the invention be limited to sealing means such as those just described, but may include arrangements wherein the actuating means are" isolated" from the gaseous medium to be treated;

The housing' T has attached to it by fastenings" I2 and extension I3 which is in turn fastened by bolts M to a'sol'id endwall l-51 A shaft I filocate'd through the extension l3 isad'riven by. somecon vent'ionalmeans as an electrical. motornotshown inthe. drawings. Shaft I16 actuates a crank mechanism 11.013. conventional. design, whichin turn oscill'atesashaft l 8 received through aguide. bearing, 26-;in atubularsectionlfl. of the housing 1.. "me right-handend ofrshaft 1a. asviewedin;

: secured -.in..a-=.;bosaiormed.on one side .otgpistonz-li.

while the inner peripheral edge of spring is fastened to the shaft l8 by a fastening 2|.

The resonating spring means which determines the natural frequency of oscillation of the piston is comprised by a series of rods 22. These rods or resonating springs have their extremities attached to the piston 4 in some convenient manner as by fastenings 26 along a region lying between the point of attachment to the piston of flexible sealing member 9 and the point of attachment of driving spring 20. A series of six of the resonating springs may for example be employed and are spaced away from the center of the piston 4 the same radial distance in every instance, as shown in Fig. 4. The resonating spring elements 22 pass through guide bearings 23, 24 and 25 to prevent bending or lateral vibration and are attached to massive wall member [5 by fastenings 21.

In operation, as the crank of the driving mechanism starts to rotate and thus oscillate shaft l8 back and forth, almost all of'this movement of shaft I8 is taken up by bending of driving spring 20 since this spring is substantially weaker than the spring system composed of'the resonating springs 22. However, when the frequency of the driving mechanism has beenso increased that it nearly equals the natural frequency of oscil, lation of the spring mass system composed of piston 4 and resonating springs 22, the amplitude of oscillation of piston 4 will increaseso that it is an appreciable fraction of the amplitude of oscillation of shaft l8.-

It will be apparent that for any specific frequency the amplitude of oscillation of piston 4 which it is feasible to obtain will be limited by considerations such as the stresses'in resonating springs 22 and piston 4, the elastic hysteresis losses in spring elements 22 and the like.

In order to obtain the maximum sound intensity in the chamber for any fixed'frequency and amplitude of oscillation 'of piston 4', the length of this chamber is chosen as'a multiple of a half wavelength of sound in the gaseousmedium to be contained in or passed through this chamber, at the frequency at which piston 4 is to be operated. Thus piston 4 is located at or near a velocity minimum, pressure maximum, position in the standing sound wave patternin the chamber at which position the desired sound intensity'may be maintained in the chamber with the minimum pistondisplacement, thus reducing the required stresses and hysteresis losses in the resonating spring elements. At this position the maximum amount of power is radiated into the chamber for the specific amplitude and frequency of oscillation of the piston.

As an example of the minimum piston dis-- placement at the velocity node, as referred to above, there may be cited the use of a device constructed in accordance with the invention-in which this minimum displacement is plus or minus .027" from rest position, that is, a total piston throw of .054", where it is desired to maintain sound intensities of 1.73 db above .0002 dynes/cm. (EMS) in the sound chamber, at 400 cycles per second. This may be contrasted with the displacement of plusorminus .430 or a' total piston throw of .960", which would be required if the piston were locatedat the velocity antinode t of the standing wave-pattern providing the'same sound intensity in the chamber.

From the above it will be seen that in obtaining a certain desired sound intensity at a certain desired frequency in *the chamber, the

the resonating spring means above described.

This is in contrast to prior art devices for treatment of liquids in resonating chambers which depend for their effectiveness on the fact that the liquid body, by reason of its physical characteristic's, may be utilized as the equivalent of a resonating spring, and is therefore an essential part of the treating means.

Having thus disclosed our invention and describedin detail illustrative embodiments thereof, we claim as new and desire to secure by Letters Patent:

1. A piston type sound generator comprising a recipro'cable piston, a relatively stationary supportjfor said'piston, resonating spring mountings fastening said piston to said support and elastically holding it stationary against motion in either direction, the resiliency of said mountings and the mass of said piston being so chosen that togetherthey constitute a spring-mass system having a predetermined natural frequency of vibration, whereby when said system is vibrating at such frequency the inertia load of said piston will H be sustained by said mountings, a driving mechanism for reciprocating said piston at said frequency, and a resilient driving connection between said mechanism and said piston to take up relative motion therebetween during starting and stopping, said resilient connection being substantially weaker than said spring mountings.

2. Apparatus according to claim 1 in which said spring mountings compriseat least one resilient rod connected atone end to said support and at the other end to said piston.

3. Apparatus'according to claim 1 in which said mountings comprise a series of resilient rods'symmetrically arranged with respect to the axis of said piston, and each connected at one end to said support and ,at the. other end to said piston.

4. Apparatus according to claim 1 in which said driving mechanism includes a crank shaft and a crank thereon, and said connection comprises a connecting rod on said crank and a spring connecting said rod to said piston.

5. A piston typesound generator for producing a standing wave pattern in a treating chamber, which comprises a reciprocable piston the face of which is adapted to be positioned at one end of said chamber, a relatively stationary support for said piston, resonating spring mountings fastening said piston to said support and elastically holding it stationary against motion in either direction, the resiliency of said mountings and the mass of said piston being so chosen that together they constitute a spring-mass system having a predetermined natural frequency of vibration corresponding to a resonant frequency of said chamber, whereby when said system is vibrating at such frequency the inertia load of said piston will be sustained by said mountings, a driving mechani'sm'for reciprocating said piston at said frequency, and a resilient driving connection between said mechanism and said piston to take up relative motion therebetween during starting and stopping, said resilient connection being substantially weaker than said spring mountings.

6. A piston type sound generator comprising a reeiprocable piston, a relatively stationary support for said piston, resonating "resilient mountings fastening said piston to said support and elastically holding it stationary against motion in either direction, the resiliency of said, mountings and the mass of said piston beingso chosen that together they constitute a spring-mass system having a predetermined naturalfrequency of vibration, whereby when said system is vibrating at such frequency the inertia load' of said piston will be sustained by said mountings, driving means for reciprocating said pistqnzat said frequency, and yielding means connecting said driving means to said piston for takingup relative 6 motion therebetween during starting and stopp ng.

CAPERTON B. HORSLEY. GORDON C. SEAVEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PK'I'EN'rs Number Name Date 1,727,861 Chapman Sept. 10, 1929 2,093,898 Taplin 'Sept. 21, 1937 2,124,983 Martin July 26, 1938 2,215,484 St. Clair Sept. 24, 1940 2,424,375 Van Allen July 22, 1947 

